View Full Version : No sync on RCA KCA118A 17" B&W portable.


farmradio
09-27-2016, 10:18 AM
Hello folks. Got a 1950's RCA B&W Model 170P034. Using KCS118A chassis. It plays well, except there is NO sync. The voltage on the screen & plate of the 6AW8 (Video output, & sync sep. are off a bit plate is too high, & screen is too low. I have a scope pic. of the 6AW8's video output plate. It does not look good to me. Swapped out the 6CU8 sync amp., & the Vid. out, but no change. The pulses on the plate of the 6AW8 do not look good either. So I'm wondering if those couplates are known in these RCA's like Philco to be a problem. Evey resistor tested is in range. Replaced some caps in the area, again with no change. Don't want to over-troubleshoot, but it's something strange. No sync pulses for both sweep oscillators. Just freewheeling along. Anything come to mind on the KCS118? Thank you.
Cathode reads 4.4V (according to SAMS should be 1.5), 4.6V on the control (SAMS shows .8V) Plate reads 175V, (should be 80). Screen reads 80, (should be 180).

DaveWM
09-27-2016, 11:09 AM
how do the voltages look on the sync sep, triode. Those are critical. If that grid is high at all, the tube will conduct video and not just the peaks (sync) which is the sync.

could also be an AGC issue, try clamping the AGC with a variable DC supply.

DaveWM
09-27-2016, 11:18 AM
looked a little closer did not see an AGC circuit. those copulate almost look like they are some kind of AGC (feeding the output from the video detector back the front end of the IF), and the scope reading from at the grid of the sync sep shows a pretty video free signal already. Maybe some kind of cancelling being done from the cathode of the video out.. I am a little lost, not seen that before.

DaveWM
09-27-2016, 11:22 AM
if you have any positive voltage at the grid of the sync sep, check that cap between test point 15 and 27, I cant read the number but it block the DC part of the video signal.

farmradio
09-27-2016, 01:42 PM
Thank you Dave, believe I did change that cap. between the test points with no change, but will double check. Will report back the sync triode portions grid reading, but I think it was high. Everytime I've hit a wall, (with Philcos anyway), it ends up couplets! Wonder?

DaveWM
09-27-2016, 02:34 PM
if its high, that will be the problem. there is a resistor to ground after that cap, cant make it out, looks like high value, but make sure it has not opened.

farmradio
09-27-2016, 03:52 PM
I'll double check, I know I've checked all resistors in circuit, wonder if a leg needs to be lifted for a more true result. I know a bad one can usually be found in circuit also by the voltage on either side too. Well not this one, because it goes to ground. I don't believe the resistors across the coils can be checked accurately either, they just read low due to the coil. Maybe lift one side or, start jumping some values across them. Got to look at the underside of the PC board too, I suppose. That is in a tough place, but must be done too to get a good look probably. The ETF has a good copy of the SAMS on-line.
http://www.earlytelevision.org/pdf/RCA-17PD9062-KCS118-Sams-418-1.pdf

farmradio
09-27-2016, 10:46 PM
The resistor to ground is ok, & resoldered the ground as a safe measure. The sync sep. control grid is -11 varies down to -6. the plate is 73V. pic. of triode control grid.

DaveWM
09-28-2016, 09:23 AM
Try feeding a composite signal into the grid of the video amp.

farmradio
09-28-2016, 10:22 AM
Called Moyer, they stocked a boatload of these back in the day by Sprague, Erie, Centralab, & RCA originals. I'm suspect of the sync one, no so much the AGC one, but they are looking for both & will get back to me in the coming days.

dieseljeep
09-28-2016, 10:30 AM
Called Moyer, they stocked a boatload of these back in the day by Sprague, Erie, Centralab, & RCA originals. I'm suspect of the sync one, no so much the AGC one, but they are looking for both & will get back to me in the coming days.

If NLA, you can easily sub them with descrete components, as all the values are listed. :thmbsp:

Findm-Keepm
09-28-2016, 10:31 AM
FYI, my August 1974 RCA price guide does not show any of the couplates listed in the Sams. :no:

farmradio
09-28-2016, 07:49 PM
Will try a composite signal.

dieseljeep
09-29-2016, 11:22 AM
FYI, my August 1974 RCA price guide does not show any of the couplates listed in the Sams. :no:

I used to be a hastle looking up part numbers for RCA and GE, as they used drawing numbers on the part. You had to go to the distributor with the model or chassis number and look up the part in the factory manual or even the Sams. Zenith, Motorola and most others used the original part number, so it was a bit easier.
Back in 1974, those parts were probably special order. :scratch2:

farmradio
09-29-2016, 03:07 PM
It also appears that K1, & K3's description is reversed in the SAMS, because the one labeled K3 (sync coupling) has no pF capacitors, & that K1 (agc), with all resistors is not used in the 118A, & verified that by not being able to physically locate it on the board. So this has K3, (sync coupling), near the sync separator, labeled K1 in the SAMS, which in fact is most likely K3 2 pF capacitors, & 3 resistors. Help! I need an RCA original service document on this. This is nuts. After that Sentinel nightmare I just did, I've got discrepancies again in SAMS.

farmradio
09-29-2016, 03:16 PM
Hello, & thank you. The part itself says CRC in a diamond logo, as the mfg., then RCA then 972182-3. Not sure who the OEM for this was.

tom.j.fla
09-29-2016, 04:17 PM
Robert, RCA KCS118a is in Riders Book 24 section 10, PDF pages 436 to 447 schematics for the 118 A,B and 118 C,D are there with all voltages and waveforms included. The info there is correct. All the best,Tom.J

Electronic M
09-29-2016, 04:52 PM
It also appears that K1, & K3's description is reversed in the SAMS, because the one labeled K3 (sync coupling) has no pF capacitors, & that K1 (agc), with all resistors is not used in the 118A, & verified that by not being able to physically locate it on the board. So this has K3, (sync coupling), near the sync separator, labeled K1 in the SAMS, which in fact is most likely K3 2 pF capacitors, & 3 resistors. Help! I need an RCA original service document on this. This is nuts. After that Sentinel nightmare I just did, I've got discrepancies again in SAMS.

Get used to Sam's being FULL of errors...At least you probably have not had the damnit I can't undo what this piece of paper had me do moment....I've had that moment twice. Once I adjusted the wrong slug on a remote reciever cause sam's had the ones for the two channels reversed in their layout. The other time I did not know how to read the bumblebee capsand changed according to the schematic. I moved and lost the originals, and come to find the schematic and parts list are different by a factor of 10, and the vert circuit they were in was off freq....I had to redesign the resistors to make it work since I did not have the other cap value on hand, and did not have any dough.

dieseljeep
09-29-2016, 08:57 PM
Hello, & thank you. The part itself says CRC in a diamond logo, as the mfg., then RCA then 972182-3. Not sure who the OEM for this was.

The logo is actually CRL, which meant Central Radio Labs, but known as Centralab. They were the early originators of the PEC, packaged electronic components. They were rather reliable, except the ones that had transistors as part the component makeup.
They were located on the northeast side of Milwaukee since the 20's, making radio parts. :thmbsp:

Findm-Keepm
09-30-2016, 02:34 PM
I used to be a hastle looking up part numbers for RCA and GE, as they used drawing numbers on the part. You had to go to the distributor with the model or chassis number and look up the part in the factory manual or even the Sams. Zenith, Motorola and most others used the original part number, so it was a bit easier.
Back in 1974, those parts were probably special order. :scratch2:

For RCA, I've got the 1974, 1979 and 1984 price guides, and a 1976 Drawing number to part number cross. I also have the Parts software to look up CTC175 - 2008 parts, and I also have several 1964-1972 RCA knob guides, and the ubiquitous Module to chassis and RCA IHVT to chassis lists. I also have a original part number to RCA part number - helpful with VCR parts, as Panasonic and Hitachi made RCA VCRs, and had the weird EQB0048RTA or so part numbers...

I've seen boxed, new RCA parts with drawing numbers not listed in the Drawing-to-part number guide. RCA issued "blue sheets" to distributors to correct/add info, but sadly, I don't have any of those.

GE also used a drawing number (early were the M128XXXXX style, and the later were 23c/73C-prefixed stuff, out of Portsmouth.) I can cross those as well, and have a couple GE price guides - 1/3 the thickness of RCA's, thanks to RCA's inclusion of their Communication Parts. Later, the two were merged - some GE part numbers went away completely, superseded by RCA parts.

RCA used the drawing number system as it was intended - the drawing number corresponded to the design drawing, on file at RCA. Even in 1983, you could call Camden for a lookup on a 50's part and they'd tell you the closest RCA part or subsequent RCA part suggested for obsolete stuff. This was the problem mostly with cabinet parts and knobs, but we called once on a detent tuner. RCA's response was a tuner with a multi-sized shaft - cut off what you don't need, and it included a guide to cut it to fit several obsolete tuner profiles. With one, you had to sub other knobs, as the indexing was different from the original.

On the other side, I have TV parts where neither the drawing number or part number appear in any RCA guides - clueless as to their application. They came from RCA when the bosses' daughter did some creative ordering to win a trip from RCA - a trip down the Nile. We swam in triplers, modules and Nipper crap for a few months after that. RCA sold us a bunch of no-demand parts too....probably for the Mural hotel-Motel sets...